Articles of footwear of various types are frequently used for a variety of activities including outdoor activities, military use, and competitive sports. The outsoles of these types of footwear often are designed to provide traction on soft and slippery surfaces, such as unpaved surfaces including grass and dirt. For example, exaggerated tread patterns, lugs, cleats or spikes (both integral and removable), and rubber formulations which provide improved traction under wet conditions, have been used to improve the level of traction provided by the outsoles.
While these conventional means generally help give footwear improved fraction, the outsoles often accumulate soil (e.g., inorganic materials such as mud, dirt, sand and gravel, organic material such as grass, turf, and other vegetation, and combinations of inorganic and organic materials) when the footwear is used on unpaved surfaces. In some instances, the soil can accumulate in the tread pattern (when a tread pattern is present), around and between lugs (when lugs are present), or on shafts of the cleats, in the spaces surrounding the cleats, and in the interstitial regions between the cleats (when cleats are present). The accumulations of soil can weigh down the footwear and interfere with the traction between the outsole and the ground.
The articles of footwear shown in the figures are illustrated for use with a user's right foot. However, it is understood that the following discussion applies correspondingly to left-footed articles of footwear as well.